This invention relates to medical devices formed from elongated wires and coils used as guidewires, e.g., for navigating narrow passageways of a body.
Generally, the distal end of a guidewire is introduced into a body by a physician, e.g., through a puncture opening, and its progress is observed by a radioscope. The physician manipulates the tip of the guidewire through tortuous aspects of the body passageways to a site to be treated. A catheter or other medical device is advanced over the guidewire to the treatment site and the guidewire is then removed, leaving the catheter in place.
In order for the physician to have a maximum degree of control over the guidewire, and to ensure the patient's safety, it is important that the guidewire be as small in diameter as possible, particularly in the tip region, but not so small as to create a danger of the tip breaking loose in the body. It is also important that the guidewire be smooth to allow ready advancement and retraction within the passageways; that the distal tip of the guidewire be highly flexible to permit negotiation of difficult turns within the body; that the distal tip be visible by radioscope; that the guidewire be stiff enough axially to be advanced by pressure from the proximal end outside the body without kinking, i.e., turning back upon itself; and that the guidewire have good steerability or torque response, i.e., the tip to-handle turn ratio should be as close to 1:1 as possible, without whipping. Most prior art guidewires compromise these desired features, e.g., trading tip flexibility for good torque response.
Fuji Terumo Co. Ltd., EP 0 141 006 describes a guidewire having a rigid body portion, a flexible distal end portion, and a tapered portion in between the body and distal portions. At least portions of the body and/or distal end are formed of a super elastic metal member, e.g., a NiTi alloy (Nitinol). A coating, e.g., an elastomer, containing a radiopaque material, e.g., barium, is disposed over the length of the guidewire so that the position of the guidewire in a blood vessel can be determined. This coating is fixed to the distal end portion so that the guidewire may be flexibly deformed within the coating.
Samson U.S. Pat. No. 4.538,622 describes a guidewire having a proximal portion formed of stainless steel wire secured at its distal end to a first coil formed of stainless steel, which in turn is secured at its distal end to a second coil formed of a radiopaque material, e.g., platinum. The distal end of the second coil terminates in a rounded tip.
Leary U.S. Pat. No. 4,545,390 describes a guidewire having a main wire or rod formed of a material that may have a high degree of radiopacity and which tapers evenly at its distal end. A coil made of a radiopaque material, e.g., a platinum/tungsten alloy, fitted over the tapered portion extends slightly beyond the distal end of the main wire or rod, and terminates in a ball weld.